In the automotive industry, vehicles are often fitted with a hitch assembly to which a trailer may be attached. Such an assembly usually includes a hitch receiver tube and a hitch bar slidably engaged within same. The bar hitch includes a ball onto which the trailer is attached. The hitch receiver tube, which is typically made of low carbon steel, is mounted on the vehicle frame by a suitable means such as brackets and the like and is normally provided at its terminal end (i.e. the end into which the hitch bar is inserted) with a reinforcing collar. Although such a collar increases the strength of the tube, various problems have been found with this structure. For example, the reinforcing collar must be welded on the bar thereby reducing its aesthetic appeal and creating heat affected zones in the material which may lead to service problems. Further, since a complete seal is usually not achieved, the accumulation of water and salt within any spaces accelerates the corrosion of the entire structure.
Various solutions have been proposed to address the above issues. One example is described by Marquardt in U.S. Pat. No. 5,203,194, which is hereby incorporated by reference. Marquardt teaches a process for reinforcing the terminal end of a hitch trailer. A significant disadvantage of the Marquardt process is the requirement for heating a tube to approximately 1800° F. before forming the tube into the required shape. As will be appreciated, such heating greatly increases the time and cost of producing each piece. Further, the heating of the tube results in de-alloying and oxidation of its surface. The deposits resulting from the heating or welding must be removed, further increasing the production time and cost. In addition, the heating of the tube deteriorates the structural integrity of the material by for instance, annealing the material, thereby resulting in weakness.
Another example is described by Roe et. al in U.S. Pat. No. 6,408,672, which is hereby incorporated by reference. The Roe et al. process describes a process for cold forming the ends of metal tubes to reinforce them. The tube is placed in a die cavity such that a portion is left outside the cavity. A mandrel is inserted into the tube. The mandrel includes a section that is adapted to bear against the portion of the tube outside of the cavity and to deform the tube. The deformation process is conducted without heating the tube and results in the tube being folded upon itself within a recess in the die cavity.
Simple cold forming processes, such as that described in Roe et. al., have a number of significant problems. One is the unpredictability of the initial direction of deformation. This means that slight deviations in positioning or structure of the initial tube, or the simple flat deforming plate, can result in the tube folding in the wrong direction or in multiple directions, creating laps, and thereby ruining the product. This is especially problematic in the corners of the tube being formed. A second problem with simple dies is that the cold-formed part is liable to stick in the die cavity. Another problem is that under the high pressures of cold forming, which are typically in the range of 165–320 tons for forming 2.5 inch square tubing with 0.25 inch walls, the die cavity is vulnerable to exploding. A further problem stems from the need for an inner mandrel that is a close fit to the inner dimensions of the tube so as to prevent it from buckling inwards during the forming process. Small amounts of the tubing metal weld to the mandrel and cause scoring of the housing when they subsequently break off. Any or all of these problems can cause costly delays and/or wastage.
Thus, there is a need for a receiver tube forming process that overcomes the deficiencies in the known methods.